Various herbicides, such as, for example, those of the sulfonamide and sulfonylurea classes are known to be active as selective pre- and post-emergent weed control agents. Many times when certain of these compounds are employed for post-emergent uses at the dosage rates usually necessary for the control of many of the broadleaf and/or grassy weeds, serious loss of some sensitive broadleaf and/or grassy crop plants occur.
One procedure to overcome the above-indicated sensitivity responses of plants to the various herbicidal compounds involves varying the dosage rate. When a reduction in the dosage rate is used to avoid phytotoxicity to the crop plants, reduced weed control is often the result.
Another procedure involves changing the time of application or modifying the ingredients used in the formulations containing the active compound. Other known procedures include treatment of the seeds of the crop plants with an agent antagonistic to the herbicide prior to planting as described in U.S. Pat. No. 3,131,509.
It has now been found that the post-emergent phytotoxicity of certain sulfonamide and sulfonylurea herbicides towards grass crop plants is reduced by admixing said herbicides with a non-herbicidal organic or inorganic acid or mixtures thereof in an amount sufficient to reduce the pH of the water diluted form of the herbicide/acid mixture to below about 5.